Merge #17985: net: Remove forcerelay of rejected txs

facb71576c net: Remove forcerelay of rejected txs (MarcoFalke)

Pull request description:

  This removes the code that supposedly handled the forced relay of txs from a permissioned peer that were rejected from our mempool. The removal should be fine, because it is dead code for the following reasons:

  * While `RelayTransaction` enqueues the inv for all peers, the inv is never processed because it can not be found in the mempool. See 4a07233076/src/net_processing.cpp (L3862-L3866)

  * Even if the peers we intended to send the inv to can somehow reply with a getdata to the never-received inv, they won't receive the tx as a reply because it was never added to the "relay memory" (`mapRelay`)

  The dead code is (obviously) untested: https://marcofalke.github.io/btc_cov/total.coverage/src/net_processing.cpp.gcov.html#2574

  This feature was (intentionally or accidentally) removed in 4d8993b346, which was released in Bitcoin Core 0.13.0. So all currently supported versions of Bitcoin Core ship without this feature. I am not aware of any complaints about this feature or actual documented use-cases. So instead of reviving an unneeded feature, just remove the dead code.

ACKs for top commit:
  hebasto:
    ACK facb71576c, locally running the unit and functional tests.

Tree-SHA512: bfceae6f2983c1510fa0649a9a63c343cbbc1c4ab3a3698039cccf454c81e58c8f5114b147ed42a1bc867da74c43a5b53764ab14f942e191b6f59079044108b5

test/functional/p2p_permissions.py

@@ -132,6 +132,16 @@ class P2PPermissionsTests(BitcoinTestFramework):
             p2p_rebroadcast_wallet.send_txs_and_test([tx], self.nodes[1])
             wait_until(lambda: txid in self.nodes[0].getrawmempool())
 
+        self.log.debug("Check that node[1] will not send an invalid tx to node[0]")
+        tx.vout[0].nValue += 1
+        txid = tx.rehash()
+        p2p_rebroadcast_wallet.send_txs_and_test(
+            [tx],
+            self.nodes[1],
+            success=False,
+            reject_reason='Not relaying non-mempool transaction {} from whitelisted peer=0'.format(txid),
+        )
+
     def checkpermission(self, args, expectedPermissions, whitelisted):
         self.restart_node(1, args)
         connect_nodes(self.nodes[0], 1)